1. Field of the Invention
The present invention relates to systems for detecting the position of an object. More specifically, the present invention relates to a method and an apparatus for using Radio Frequency Identification (RFID) tags to determine the position of an object.
2. Related Art
Computers often need to know the position of an object in the physical world. For example, interacting with a computer system often involves moving a mouse, a trackball, or some other physical object. In addition to user interaction, there are many other contexts in which computers need to know the position of objects in the physical world. For example, logistics systems need to track the movements of goods through warehouses, and assembly robots need to determine the position of cars as they move down the assembly line. Applications of such knowledge are nearly countless, because knowing the position of objects is a fundamental requirement for interacting with the physical world.
One technique for determining the position of a physical object is to modify the object to so that it is able to track its own position, and to report its position through a wired or wireless connection. While this technique is useful for some applications, it is expensive to modify an object in this way. Moreover, the object must contain a power supply, such as a battery, which further increases bulk or tethers the object through a physical connection.
Another technique is to use a video camera to survey a scene, and to use object recognition software to identify and determine the location of objects within the scene. However, this technique is expensive and requires line of sight access to the camera.
Moreover, creating software that accurately detects objects is a daunting task because of hidden surfaces and similarities between objects. For example, in a warehouse containing boxes of similar size, if the camera cannot see the side of a particular box with distinguishing markings, the system cannot identify the particular box.
A relatively inexpensive technique for determining the position of an object in the physical world is to attach a Radio Frequency Identification (RFID) tag to the object. RFID tags are relatively small (some are smaller than a nickel), inexpensive, and do not require a power source. However, existing RFID tag readers cannot pinpoint the exact location of the object. Rather, they simply report the presence or absence of a tag in their field of sensitivity.
Hence, what is needed is a method and an apparatus for using RFID tags to determine the position of an object.
One embodiment of the present invention provides a system that uses Radio Frequency Identification (RFID) tags to determine the position of an object. During operation, the system receives signals from an array of RFID tags at an RFID tag reader, wherein a mask of known size and shape is interposed between the array of RFID tags and the RFID tag reader, thereby obscuring signals from a subset of the RFID tags. Next, the system determines the position of the object by analyzing the pattern of obscured RFID tags, wherein the analysis is based on a known spatial relationship between the object, the mask and the array of RFID tags.
In a variation on this embodiment, the array of RFID tags resides at a fixed location and the mask of known size and shape is coupled to the object. In this way, when the physical object is interposed between the array of RFID tags and the RFID tag reader, the mask obscures the subset of RFID tags.
In a further variation on this embodiment, the object contains a separate RFID tag that facilitates in identifying the object.
In a variation on this embodiment, the mask of known size and shape resides at a fixed location and the array of RFID tags is coupled to the object. In this way, when the mask of known size and shape is interposed between the object and the RFID tag reader, a pattern on the mask obscures the subset of RFID tags.
In a further variation on this embodiment, identifiers received from RFID tags in the array of RFID tags facilitate in identifying the object.
In a variation on this embodiment, the system analyzes the pattern of obscured RFID tags to determine the orientation of the object.
In a variation on this embodiment, each RFID tag in the array of RFID tags is a passive, unpowered circuit that transmits a unique ID in response to an RF signal.